1. Field of the Invention
Embodiments of the present invention relate to linear actuators and methods of operation of linear actuators and, more particularly, to linear actuators and methods of operation of linear actuators for use in aircraft.
2. Description of the Prior Art
Actuation of safety critical mechanisms in safety critical systems or equipment needs to achieve a high level of reliability. It is generally known to use hydraulic actuators in aircraft, for example, to operate landing gears and/or flaps and ailerons and so on, due to their reliability. Hydraulic system failure is usually caused by leakage of hydraulic fluid, and the system fails to a freely moveable state without jamming. In the case of hydraulically actuated landing gears, this allows the gears to be lowered for landing in spite of a system failure.
The utilization of electromechanical actuators is advantageous because they are light in weight and can be incorporated into an aircraft simply and powered using the electric power distribution system within the aircraft. However, electric motors have a significant seizure failure mode, whereby they tend to fail to a jammed state, which prevents backup systems from becoming effective.
Aircraft safety regulations require high integrity and invulnerability to single failures for those items of equipment whose failure could lead to catastrophic consequences. Landing gear actuators must meet this criterion and jam vulnerability has prevented electric actuation from being used.
Known failure-tolerant linear actuators require two separate actuators each having a disconnect device, wherein, in the event of a jam, the jammed actuator can be disengaged and the other actuator can be used.